Hospitals are being overwhelmed by large numbers of obese people asking for radical surgery to reduce their appetites, with doctors turning away patients because the queues are so long.

Specialists say they cannot meet the huge demand for operations to reduce patients' stomachs so they are forced to eat much smaller amounts of food. Some NHS trusts have raised the limit of how much people must weigh before being considered for surgery in a bid to restrict patient numbers. The surgery can transform the lives of people who are severely obese and risk developing complex health problems, such as heart disease, diabetes, high blood pressure and joint pain.

'The situation is really dire,' said Dr Nick Finer, an obesity specialist at Addenbrooke's Hospital, Cambridge. 'The NHS must somehow find the money to treat these patients, who otherwise face the prospect of a lot of disability and a premature death. In my region, there are three counties which between them are going to fund us for 60 operations this year. The number should be around 500 operations. We simply would not tolerate this kind of hard rationing if it was about cancer care.'

Normally, surgery is considered for anyone with a body mass index (weight in kg divided by height in metres squared) over 35. But with obesity rates rocketing and the waiting lists for surgery getting longer and longer that some primary care centres have started to say that patients must have a BMI of 45 or more before they can be considered. A man who was 5'8" tall would have to weigh 16st 6lbs to have a BMI of 35. To have a BMI of 45, he would need to weigh 21st 2lbs.

A Swedish study recently showed that the surgery increases a patient's chances of survival by 31 per cent over five years.

The most common operation, know as laparoscopic gastric banding surgery, involves placing an inflatable band around the top of the stomach. This creates a small gastric pouch which limits food consumption and creates an earlier feeling of fullness.

During the months that follow the operation, patients become accustomed to eating a reduced number of calories and tend to stick to their new habits even three years after surgery. The procedure results in average weight loss of 20-25 per cent.

The surgery costs £8,000, but studies show the amount it costs is saved in two years because patients no longer need treatment for related conditions.

A survey by GPs' magazine Pulse of around 30 hospitals found that nearly nine out of 10 consultants responsible for obesity referrals lacked the resources to cope with an increase in referrals from GPs.

The NHS is thought to spend around £500m a year in treating obesity, but the majority goes on treating secondary diseases linked to it. Less than five per cent is spent on surgery or appetite-suppressant drugs to reduce obesity itself.